Stretchable fabric and method of making same from multiplicity of yarn ends



Sept. 24, 1957 R. F. STUEWER STRETCHABLE FABRIC AND METHOD OF'MAKING SAME FROM MULTIPLICITY OF YARN ENDS Filed Feb. 10, 1955 frese? J' ATTORNEYS United States Patent Oliice 2,807,073 Patented Sept. 24,V 1957v STRETCHABLE'FABRIC M ETHGDE 0F MAK- Application February 1'0`, I955`,.Seri`alfNo. 487,255

Claims. (Cl. Z876) This invention relates to ay textile articlehaving stretching. properties superior to those exhibited by articles. prepared from-untreated yarn ends, and to the method of prodlucingsuch article.

When synthetic fibers of the polyamide and polyester types, and in. general theV polymer synthetics which are formed by extruding a liquid through a nozzle, hardening. and then stretching. the" filament, are subjected to setting operations atr correlated temperature and time con ditions, they thereby attain the capacity' of returning toward the shape existent during'the setting operation, in event of. later mechanical twisting or untwisting', for example. Such yarns can be referred tol as. comprised of stretched. microcrystalline polymers. When itis dev sitedto increase the stretchability offabricsmade from` multilyarns, it has. been proposed to= set them in twisted form, so that the fabric is thus composed of individual knitted courses, weftsor warp's, which. have curls or twists in the filaments. In knitted fabrics there is a permissive stretchability in the loops formed in the knitting,y and. if a. monol or multiiil yarn is` employed which hasa curled or. helical form, a further stretching ispermitted by the movement of the yarn' fromf helical to straight form under the force applied.

However, such helical yarnsare' more costly to make than straight filament yarns, and' there are dit`n`culties' in preparing fabrics from yarns which have been twisted to confer a helical form, due to socalled live1iness.2 Snarls may occur during.v the knittingl and defectivel articles result. Machine attachments and devices are known, in. whichv such lively yarns may be handled by maintaining them in a relatively uniform. stretchedI condition; but even in` such cases the machine adjustments are very critical, operation is difficult, and the output per machine is reduced.

It has been found that. stretchable fabrics can be made from yarns which are in: a non-lively or dead condition during knitting or weaving, and thereafter are further treated to confer upon` them the desired characteristic'.

When a length. of a dead or non-lively monol yarn of. pre-set behavior istwisted about its axis, the effect is not visible in: av cylindrical lament while it remains under endwise tension; but it canl be assumed that the previous longitudinal molecular linkages at thesurface, for example, have beenA distorted int-o'l helical lforms. When: the endwise tension. is released with the ends. held against untwisting the length tends to fetch up into a helixor one or more lateral loops with entwined bilar stems. When one end is released, it tends to rotate'ab'out the longitudinal axis, to release the twist. If the yarny isv subjected to a setting operation while' held in: such twisted condition, its capability of unwinding'is reduced.. For example, if a. right-handV twist of 50'turns per inchV is given such yarn, and setting. accomplished in' water at', say, l80 degrees F., the yarn will untwist by, say', 13 turns per inch (residual 3-7 turns: twist) andl then acts dead or without liveliness although the original. condi tion hasnot-been gained.. In generaletherequired' amount off untwisting'depends inversely upon the setting tempera* ture, other' conditions' being the same: for example" the dead condition may occur at 14' turns untwisting (3`6 turns residual) after treatment at 17 0' degrees Fi, or at" l2" turns untwisting- (38.turns residual) at 200 degrees F.'

The behavior of asynthetic yarn is' largelydetermined' by its history. Its disposition upon heating above' roomy temperature, when without external'stress, is' to assume the shape or relative position of the parts existent during the last prior setting operation: and it may' develbpf in-l tern'all stresses when detained against free return tti-such'- shape or relative position. ln general, the elfect of setting operation can only be totally dissipated by' a' treatment which is more rigorous than the' setting it'selfi For example, a yarn which has been twisted and set' at 200 degrees F. inl hot water undergoes achange ofr shape'-l or relative positioning whichr is not' completely climinat'ed by alater immersion in water at such temperature; and in practice some of the imposed twist will not'pb'e dissipatedy by treatment at 212 degrees F. l

It has been` found that' a yarnv having' a pre-set behavior imposed at a relatively high temperature, which' is then given a right-hand twist ofA 50 turns per inch and then'` set' at' a' lower temperature while held in Asuch twisted state, c'an then be broughtto a non-lively' or dead condition by partial untwisting by, say, ll turns; and,v furthermore, whenA the yarn inthis non-lively condition'is again subjected to a heat-treatment, it is activated and; tends to u'ntwist further by, say, 12 additional turns, thereupon exhibiting a liveliness condition corresponding' toaleft-hand twist of 12' turns. Similarly, if the originali twisting is left-hand, and the same succession of operations is performed, the'inalV product exhibits a livelinessr condition corresponding to a right-hand twi'stof 12' turns. The amount ofw re-assumed liveliness can be determined' by the conditions of the successive heat treatments. v

It has thusl beeny found feasible to produce stretchability ina fabric by twisting and setting a yarn, effecting untwisting until the yarn is non-lively or dead",' in which condition it can be used in making a fabric, and then subjecting the fabric to a further treatment for developing liveliness in the yarn' by a release of a further part of the previously set state.

This behavior is likewise exhibited when a yarn A is given an original right-hand twist withI a further treatment as just described, and an original yarn B is given the' like treatment with the left-hand original twist: and that when a third monol yarn C which has not been pre-set and pre-twisted is also introducedI during. the forming of the fabric, the fabrication can. be accomplished with the three yarns A, B and C in dead condition so that knitting or weaving is easy; Thereafter, the further treatment produces release in the yarns A- and B` so'that they develop liveliness: and the same treatment also accomplishes a setting in yarn C, so that it. likewise responds' tostretching by its elastic tendency to return tothe prior condition.

Due to the importance of history of the yarn, itis preferred tofsubject the yarn as received to a pre-setting treatment, prior totwisting, which'. is more' rigorous than any later treatment to be' given. This fixes in the ma.- terial a condition of straightness, in line with-whatv is sometimes called memory Thereafter, when a twisted and re-set yarn is again treated` in a relaxed"V condition,v it tends to return toward the original relative positioning of parts imposed byl the pre-setting.

EXAMPLE I A lfdenier nylon mon'ofl, as received, was subjected without twisting to a pre-setting at 265" degrees F. under steampressure (25 lbs. pressure).l for 20- minutes. A part of the yarn was twisted' to= the-right on a machine adr justed for 51 turns per inch and then set at 200 degrees F. in moisture-saturated air while held at such twist. The yarn had liveliness; but this was removed by mechanically untwisting (to the left) 12 turns per inch, and the yarn was Wound on a bobbin or shaft, and then rewound on a knitting package. A specimen taken immediately after untwisting indicated a tendency for reverse (rightward) twisting, that is, an excess untwisting had been accomplished. About 4 hours after the untwisting, the specimen had the same appearance and deadness as in the pre-set state. Another part B of the yarn was twisted to the left with the machine adjusted for 50 turns per inch, set at 200 degrees F. in moisture-saturated air while held at such twist; mechanically untwisted (to the right) 12'turns per inch, and then likewise wound and rewound to a knitting package. A specimen thereof also indicated immediately an excess of untwisting, which had disappeared in about 4 hours time so that yarn B likewise had the same appearance and deadness as in the pre-set state. At this time, yarns A and B were employed in knitting successive courses, followed by knitting with a non-pre-set yarn C of the same 15 denier nylon monol, which had not been treated by twisting or setting. Other specimens of yarns A, B and C can be employed in multifeed knitting systems, with the first feeding device delivering yarn A, the second feeding device delivering yarn B, and the third feeding device delivering yarn C; this succession being repeated. The fabric had the appearance of being knitted from yarns of dead character. The fabric was then subjected to a treatment in boiling water for 1 to 10 minutes, whereby a release of set was accomplished in yarns A and B, and a setting operation was accomplished on yarn C. The major effect occurred within 1 minute. Therewith yarns A and B developed a liveliness, with shrinkage of the knitted size: and yarn C received a setting in its looped condition, so that it exhibited less stress and tendency to straighten than in the fabric as knitted. The fabric could be stretched from its shrunken size after treatment, to essentially the same length as prior to the set-releasing treatment.

In general, the kyarns A and B tended inherently to release a couple turns of the potential for residual twisting effect in a few hours, and hence like excess mechanical untwistings are preferred so that the yarns A and B will be dead at the time of knitting. This automatic release is essentially complete after 24 hours; so that stored yarns do not exhibit thereafter a continued tendency to become lively from the dead condition. The set-releasing treatment can be varied. When stockings are knittedand seamed before the releasing treatment, the release can be effected by immersion in boiling water, by immersion in a dye bath at 16() degrees F., or by loose boarding and placing in a chamber with steam at 240.degrees F. for-a minute. Also unseamed stockings have been heated in steam at 240 degrees for a minute, and then seamed. In each case, a satisfactory liveliness developed in the fabric.

,The operations can also be conducted with a multifeed knitting system, in which a rst feeding device serves to deliver several courses of yarn A, followed in turn by the second feeding device delivering several courses of yarn B, and in turn by the third feeding device delivering several courses of yarn C. These successive groups of courses thus can provide visually apparent bands in the fabric.

Likewise, after pre-setting, twisting, twist-setting of the yarn A, two or more ends of such yarn, for example with two right-twisted ends, may be paired preliminary to the untwisting to dead condition and then untwisting: wherewith the resultant composite yarn has a dead behavior resultant from the compensatory effects of the yarn ends upon one another during the untwisting, in conjunction with the tendency of each yarn to untwist. VA similar action may be taken with yarn B, for example with two left-twisted ends, noting that the several twistings and untwistings are respectively opposite to those employed with the ends for yarn A.

EXAMPLE II A 15 denier nylon monol was subjected without twisting to pre-setting at 212 degrees F. in saturated steam; right-twisted 5l turns per inch, set at 180 degrees F., and mechanically untwisted (to the left) by 10 turns per inch, whereby a non-lively yarn A was obtained for knitting. Yarn B was prepared in the same fashion, but with original twisting to the left. Yarn C was prepared by taking the original monol, without pre-setting or twisting. The yarns can be knitted with a three-carrier system, and the fabric treated in hot water at 180 degrees, thereby shrinking and becoming lively.

lngeneral, for a given condition of pre-setting by prior history, the closer the setting temperature approaches the pre-setting temperature, the less the liveliness of the set material. Thus, with the above pre-settings at 265 and 212 degrees F., setting of the twisted yarns at successively higher temperatures will give yarns with different and successively lesser amounts of liveliness which are thereafter eliminated, under this invention, by correlated untwisting. When the pre-setting was at 265 degrees F., under the first example, setting at 200 degrees left 12 turns per inch of relative liveliness, with 39 turns residual in the dead material and potentially in major part available for re-establishing liveliness when the relaxed yarn A or B was heated after the knitting. If the twist-setting is at a lower temperature, the liveliness is greater, and a larger number of turns per inch must be untwisted to attain a non-lively condition. If the twist-setting is at a higher temperature, less turns need be untwisted to attain nonliveliness.

A like relation exists between the conditions of twistsetting and set-releasing for yarns A and B. A yarn as in Example I, which has been twisted and twist-set at 200 degrees F., and then untwisted to dead condition, shows different amounts of development of liveliness in the fabric at different temperatures. For examples, at degrees F., specimens underwent release of l0 turns with 29 turns still residual: at 180 degrees F., release of 16 turns with 23 turns residual; at 212 degrees F., release of 22 turns with 17 turns residual; at 240 degreesin steam, a release of 26 turns with 13 turns residual. The released turns represent the liveliness which can be conferred upon the fabric and yarns from the dead condition at knitting.

Comparably, when the twist-setting wasylat degrees F., with untwisting 14 turns to dead condition, the yarn specimens underwent a release of 13 turns (24 turns residual) at 140 degrees F.; a release of 18 turns (19 turns residual) at degrees F.; and a release of 26 turns (11 turns lresidual) at 212 degrees F.

As a further comparison, yarn was pre-set as in Example II (212 degrees F.), twisted 50 turns, and specimens were twist-set at temperatures of 180, 169 and 140 degrees F. Ten turns per inch were untwisted from the specimen twist-'set at 180 degrees, and 12 turns from the others, to get an essentially dead condition. All specimens were then subjected to set-release in boiling water (212 degrees F.) for 10 minutes, after a brief subjection to wet atmospheric steam for convenience to avoid snarling. The specimen twist-set at 180 degrees had a release of 22 turns per inch (18 turns residual); that at 160 degrees, a release of 25 turns (13 turns residual); and that at 140 degrees, a release of 27 turns (11 turns residual).

The required increment of stretchability, economic conditions, andthe schedule for dyeing, boarding and like after-treatments of the fabric, determine the selection of the temperatures'to be used.

When fabrics, from yarns pre-set at 212 degrees F. in moisture-saturated air, were exposed to steam at 15 lbs. pressure (250 degrees F.), the fabrics stretched less distances and had lost some resistance to stretching, as

compared with those in which the release was effected at lower temperatures. The pre-setting can be at a tem perature of 212 degrees F. and the twist-setting at temperatures as low as 140 degrees F., and yet stockings knitted from the partially untwisted yarns can be subjected to boarding under 15 lbs. steam pressure (250 degrees F.) after the releasing treatment, and exhibit significant stretch properties. Such stockings exhibit a somewhat less resistance to stretching than those made of yarn pre-set at 265 degrees F. (25 lbs. steam pressure) and given the same twist-setting treatment, with a boarding at l lbs. steam pressure.

It has been found that the amount of liveliness or tendency to relatively untwist exhibited by a monoiil which has been twisted and twist-set has very slight increase with the turns of twist introduced: but is more critically dependent upon the twist-setting temperature. Thus l5 denier nylon yarns can be subjected to twisting through 30 to 100 turns per inch and conditioned or twist-set at 160, 180, 200 and 212 degrees F. in moisture-saturated air or steam; and the yarns untwisted to a,dead state. Yarns twisted by 30 turns, and twist-set at 180 degrees F. required -12 turns untwisting, with a residual 18-20 turns remaining in the dead yarn: ya-rn twisted 65 turns, and twist-set at 180 degrees F. required 12-14 turns untwisting, with a residual 51-53 turns left in the dead yarn. In each case, heating of the fabrics in boiling water resulted in the release of the major part of the residual twist, as indicated by the values above: but it will be noted that yarn originally twisted 30 turns can develop'20 turns of liveliness at most, while that twisted 65 turns can develop up to about 40 turns of liveliness without employing strenuous releasing conditions.

In practice for knitted stockings of nylon of around 10 to 15 denier, a range of 30 to 60 turns per inch of original twist, with twist-setting at 160-180 degrees F., and the removal of 8-16 turns for a dead condition, represent presently preferred commercial practices in preparing yarns A and B, which respectively were twisted right and left after the pre-setting. For other fabrics,

i e. g. woven crepes, higher final liveliness is desirable, and

can be attained by higher original twists, up to 100 turns per inch for denier yarn for example, a more extensive twist-setting so that less turns need be removed to produce a dead condition, and by more severe set-releasing temperatures employed upon the fabric while it is in a relaxed condition.

It has been found desirable to effect pre-setting without significant tension in the yarns, so that shrinkage may occur. This can be accomplished by winding the yarns upon tubes having collapsible corrugated coverings and treating the yarns thereon, or by difference of the yarn speeds at entering and leaving the pre-setting region.

The time required for the release of residual turns of `twist is very short. A large effect occurs as the material enters the temperature zone (e. g. hot water), and only a small increase occurs after the first minute. In tests with single strands, it was found that there was no significant difference between l0 and 30 minutes treatment.

A characteristic of this invention is the employment of yarns A and B which areessentially dead and hence easy to knit Vor weave, but which have an inherent potential to develop liveliness upon a treatment of the fabric, resulting in tendencies of the individual yarns to twist and skew, but with this tendency compensated by the presence of right-hand and left-hand twisted yarns adjacent one another in the courses or bands; andin the employment of a yarn C which does not have afpotential or stored elect by which it exhibits a liveliness due to release'of such potential upon the treatment of Ythe fabric for re'- leasing the set in yarns A and B. Yarn C, however, undergoes a setting during such treatment, as distinguished from the set-release in yarns A and B, and therebyY it accepts a position in the fabric which is exhibited by elasticity of the yarn C when the'fabric is stretched.

IIn tests made upon unknitted monol yarns, to deter,- mine the releasing action, a vertical tube was provided vand connected toa source lof steam or moisture-satinated air for upward flow. Small skeins of 10 threads, and single loops, were formed 44 inches in circumference; a weight of 0.25 gram was placed in the bi-ghtyand the skein or loop slowly lowered into the tube, ywith counting of the number of twists made by the skein or loop.

'In one series of tests, 15 `denier nylon yarn was preset for 20 minutes by steam -at 25 lbs. pressure, with allowed shrinkage; followed by inserting .the number of turns indicated below as Twist, and conditioning, at the temperature (F.) stated as Twist-setting. Lengths of the yarn were then mechanically untwisted 'by the num lber of turns stated as Twist removed. The skeins were made, lowered into the tube and held for ten minutes: the liveliness thus developed, being the turns developed Lby the twisting skeins, are in the column Skein,V and -by single loops -similarly handled, in the column Loop The specimen yarns were also employed in knitting, in the twist-set and partially untwisted state: and the results are given in the Knit column by the reference S indicating satisfactory knitting with ordinary machines and adjustments, U indicating Yknit-ability upon special equipment to avoid snarls, and C denoting that care was needed in knitting upon standard machines. Yarn remaining on the knitting packages was tested, after'two weeks from the twist removal, to determine the liveliness at that time; and the values are reported in the column After 2 weeks. Y

Table I Total turns Twist Twlst- Twist- Knit After f setting removed 2 weeks Skein Loop 200 l2 213 382 S 0 12 282 554 C 2.2 12 210 300 S 0. 3 180 10 268 B38 C 1.5 160 12 235 348 S 1.2 160 10 245 360 U 1.9 180 14 226 380 S 0 180 1l 242 415 S 1. 7 160 12 248 463 U 2.0 212 l2 206 397 S O 180 12 290 547 S 1.6 212 12 254 490 S 0.3 212 10 277 '522 C 2.2 180 14 336 665 U 1.3

The knitting tests indicated that the liveliness values found by the test for 10 strands were not strictly cornparable, if yarns of considerably different twists are involved. Thus a 51 turn specimen showed a liveliness of 213, but gave a better fabric than a 30 turn specimen with a liveliness of 235, when the fabrics were given like releasing treatments.V

i The liveliness values found with single loops appeared to bebetter indications, as to t-hefab'ric which can be made, than the values for the skeins.

The liveliness in some of the yarns, so that special knitting conditions were desirable, was due to the selection of an untwisting action of the throwing machine which did not bring the partially untwisted yarn to a dead condition at the time of knitting. Obviously, such effects can be avoided by a dierent selection of the number of turns for untwisting following a given treatment. This is corroborated by the last column in Table I, showing the liveliness present two weeks after the mechanical untwisting, from which it will be noted that yarns having livelinessgof 2 turns or over per inch required special care or special equipment to `avoid snarls, and that even lesser liveliness may cause diiculty. The liveliness of the yarn, at completion Iof the twist-setting, can beclosely estimated by observing its behavior in a twist-tester, using lengths of l0 or 20 inches .and observing its tendency to form loops after a given number of turns have been removed and then re-twisting or further uri-twisting until the yarn appears dead; and then untwisting the rest of the yarn by a corresponding number of turns per inch plus, for example, about 2 turns per inch for 15 denier, 5l turns yarns to provide for the .automatic adjustment in the yarn during the time between mechanical untwisting and knitting.

The fabric as knitted is composed of yarns which have inherent potential ability to become lively upon the later treatment, along with yarns which have no such potential .as employed in the knitting or weaving machine. In the foregoing, these yarns have been described as of the same sizes, with yarns A vand B having individually undergone respective treatments by pre-setting, right or left twisting, setting and untwisting. The yarns A and B can 'be employed with the non-potential yarn C by a multiplefeed system for providing successive courses in a circular knitting machine, for example: or providing successive pairs of courses in a flat bed knitting machine.

. lIt is also feasi-ble to employ the yarns in other fashions, by which the advantages of their differential behaviors can be employed in producing a fabric which has excellent elastic stretching properties.

vAs an example -of practice, with yarns in any of the examples above, a stocking may be knitted by three carriers with yarns A, B and C, and then the welt or heavy sect-ion is formed by these carriers with, for example l5 denier yarn, and a fourth carrier having a 20 denier thread whichhas not been treated, i. e. the yarn in the fourth carrier -is non-potentia in having 'been so prepared that it is ready to respond to the treatment of the fabric which is accomplishing the release of a potential effect in yarns A and B, but therew-ith assuming a relatively stressed condition due to the development of liveliness in yarns A and B, together with a setting of this yarn C -in the shape thus produced. A first course can then be deformed with the 20 denier end and a lefttwisting l5 denier end of yarn A laid together in the course; with a next course containing the 20 denier end and an untwisted l5 denier end of yarn C; and a third course containing the 20 denier end and a right-twisting denier end of yarn B. The courses are then repeated in order. The foot of the ystocking can be made in the ysame fashion. When this fabric is subjected to a treatment with heat and moisture, yarns A and B undergo a set-releasing, and yarn C along with the denier yarn laid by the fourth carrier, receive a setting effect. The yarn C, and the yarn for the fourth carrier, need not be nylon. For example, the yarns A and B can be employed in nylon or a like material having the characteristic of becoming set with permissive set release later, whereby to establish the lstretch property, wh-ile the other yarn maybe of untreated nylon, silk, or other fiber, for conferring other ldesired properties upon the fabric made. As an example, the fourth carrier described above may have its 20 denier yarn provided by multil nylon, whereas yarns A, B and C are of monoiil nylon. Cotton or wool can thus lbe introduced in knitting mens socks, with the yarns A and B serving for establishing the stretch properties.

EXAMPLE III Practice with multifilament yarns can be conducted for example by subjecting a 30 denier 10 filament nylon yarn to pre-heating for 2O minutes at 265 degrees F. in moist air, while wrapped on tubes covered with corrugated paper to permit shrinkage. One end of such yarn was then twisted 5l turns to the right, twist-set at 200 degrees F. in moisture-saturated air for one hour, and then mechanically untwisted 21 turns, to give a dead yarn A which was then sized. A similar yarn end B was prepared but with the first twist to the left, and with the untwisting to the right, to give a dead yarn, and followed by sizing. `A third end of the original yarn, without presetting, was twisted 30 turns left and then twist-set at 180 degress F. to form a yarn C of non-potential type. Each of the original ends had a minor original twist,

but the effect of this was not apparent in the final result. The three yarns were knitted into a hosiery fabric, with successive courses being knitted from yarns A, B and C on a conventional three-carrier knitting machine. The stockings had the appearance of conventional three-carrier fabric when removed from the machine. Upon immersion of the stockings in boiling water for one minute, the potential twist of yarns A and B was released with shrinkage of the stockings; yarn C responded to the shrinkage and twisting of yarns A and B and a setting effect upon the yarn C, and a highly stretchable fabric was produced. The stockings were then dyed and finally boarded at 240 degrees F. in a steam chamber.

In work with multifilamen't yarns, where the appearance of broad bands of different light reflection, or streaked appearance, is undesirable, it is preferred that the final twist in yarns A, B and C be essentially the same, and one or a few courses be formed with each successive yarn end A, B or C, during the fabrication; so that the final product does not exhibit bands having differing light reflection due to the differences in the final twists. In this Example III, it will be noted that yarn C has been given a conventional treatment, without the pre-setting as employed for yarns A and B. Where a striped appearance in a fabric is desirable, in band form, the final twist may be of different amounts, and attained by having the yarns at the time of knitting with differing potential twists or conventional twists therein.

In the accompanying drawing, Fig. l is a greatly enlarged illustration of a part of a fabric made from three yarns laid in successive courses in accordance with this invention.

Fig. 2 is a diagrammatic showing of the steps of treatment of the three yarns.

In Fig. l, the portion of fabric is assumed to have been knitted with a first course of a yarn C of untreated monoiil nylon, with forming of the usual loops therein, illustrated in the drawing by absence of shading along the filament, these loops being somewhat more open than shown in Fig. l, in the as-knitted condition, as is known to those skilled in the knitting art. The next lower course is provided by a left-twisting yarn A of nylon monofil which is distinguished in the drawing by the vertical designating lines thereon. The third course is provided by a right-twisting yarn B of nylon monofil, its loops being designated by horizontal lines. For the rest of the fabric, the courses of yarns C, A, B are repeated. After knitting, the fabric was subjected to the treatment whereby the potential effects in yarns A and B underwent a release, and therewith the loops of yarns A and B have respectively twisted toward the left and right, with each yarn having a final position resembling a helix, with the loops tending to turn over, so to speak, from the more planar position occupied by the loops of yarn C, therewith causing a contraction or shrinkage in the fabric, which contraction later can be utilized in stretching back to the size normally permitted by a similarly knitted fabric in which all of the courses are of a treated yarn such as yarn C. During this treatment, the yarn C has undergone a setting in the condition occupied in the knitted fabric, with a modification due to the shrinkage as the liveliness develops in yarns A and B. Therefore, upon lengthwise pulls between the right-hand and left-hand ends of yarns C in Fig. 1, the fabric will stretch, but the elastic resistance produced by this setting of yarns C leads to a property by which yarn C assists in the production of a high stretching effect in the fabric.

In Figure l, the courses of yarns A, B and C provide single-course bands from yarns of different characteristics at the time of knitting; but it will be understood that fabric may be prepared in which such a band may comprise two or more successive courses of yarn of one given characteristic, followed by a band of one or more courses of yarn of a different characteristic, and then by a third 9 band of one or more courses of a yarn of a third characteristic. Y

It is particularly to be noted that one-third of the yarn employed in Fig. 1 is of non-potential monol nylon, for yarn ends C; while the yarn ends A and B have been treated by pre-setting, twisting, vand partial untwisting and are of potential type. Therefore, one-third of the material is less expensive than the rest, so that there is a reduction in cost for the final fabric over its manufacture totally of either lively yarns or of yarns having potential liveliness. Yet all of the yarns employed can be knit in the dead condition, with release ofpotential liveliness in yarns A and B, and the setting of yarn C in a form where it exhibits elastic stretchability.

In Fig. 2, the treatments for the three yarns of Fig. l are set out by a diagram. Yarn A is subjected to a presetting operation 20, -followed by right-hand twisting in an operation 21 and a twist-setting operation 22. Yarn A is then partially untwisted in an operation 23 with an excess of untwisting so that any residual automatic untwisting is compensated for and after a period of `a few hours the yarn is at a dead condition. Yarn B is-smilarly subjected to successive operations of pre-setting 30, left-twisting 31, twist-setting 32, and a partial untwisting 33. Yarn C may be used in the non-potential condition as received from the manufacturer. The yarns A, B and C are then introduced into individual carriers in a knitting machine and knitting performed as indicated at 40. The fabric is then subjected to the set-releasing and setting treatment 41 as described above, and then has a form as indicated by Fig. l.

It is preferred to perform the heating operations in steam or moisture-saturated air. However, other vapors and gases may be employed; noting that oven heating requires higher temperatures forproducing a given effect, and `that the material must not be heated at any point lto the adhesive or melting temperatures of the synthetic base.

Other stretched synthetic fibers, such as polyesters, give comparable results.

A polyester (Dacron) multil yarn of 40 denier (34 filaments) can be pre-set for 2O minutes in steam at 25 lbs. pressure while free to shrink. Ends A and B of such yarn can be respectively twisted right-hand and left-hand, with 20 to 100 turns per inch', and then twist-set. The yarns A and B are then mechanically untwisted, to give a substantially dead yarn at the time of knitting. The yarns A and B are then knitted with non-potential yarn C, to form fabric: the goods upon immersion in boiling water become highly stretchable, by release of the residual or potential twist effect in yarns A and B, and the setting in yarn C. In one specimen of Daeron, twisted 50 turns, and twist-set at 212 degrees F., 9 turns were removed, and a liveliness of 32 turns was produced upon the release. In another specimen, twisted 50 turns and twist-set at 180 degrees, with removal of l2 turns, a liveliness of 30 turns was developed. In a third specimen, twisted 100 turns, and twist-set at 180 degrees F., 14 turns were re` moved, and a liveliness of 73 turns developed upon release.

The effects upon yarns of dilferent sizes are comparable, account being taken of the size. Upon pre-setting monolils of 10, 20 and 40 denier for 20 minutes in steam at 25 lbs. pressure, twisting 5l turns per inch and twistsetting at 180 degrees F. in moisture-saturated air (sometimes referred to as 180-180, as the wet and dry bulb thermometer readings are the same), the apparent liveliness was different. The 10 denier yarn became dead when untwisted 13 turns, the 20 denier yarn at 10 turns, and the 40 denier yarn at 8 turns.

The effects are likewise obtainable with multifl yarns, as indicated by the above example with polyester yarn. Such multitl yarns are presently delivered commercially with about a half-turn per inch, usually left-hand; and when 20 orrrnore turns per inch are given to it, the effect of such original twist is insignificant whether the further 10 twist is right or left hand. When an original -multiil Yarn of 20 denier (7 filaments of about 3 denier each) is pre@ set for 20 minutes in steam at 25 lbs. pressure, and then twisted 51 turns and twist-set at 200 degrees in humid air, the liveliness required removal of about 14 turns per inch: that is, more turns were removed than with a monofl of 20 denier. Another part of the same original yarn was pre-set, twisted in the opposite direction, twistset, and about 14 turns per inch removed. These yarns A and B are potentia in having therein a twist-set effect which can bev released by a subsequent treatment, and are present in a dead condition for knitting along with anonpotential yarn C, which for this example may be a conventionally treated yarn of the same original stock, with 35 turns of left-twist. The yarns A, B and C were then knitted in successive courses. The yarns knitted satisfactorily, veach being essentially dead The fabric was treated in boiling water and developed liveliness in the yarns A and B, and a satisfactory stretch in the fabric.

The amount of original twisting desirable for a given case depends upon the size of the filament, and the purpose of use. It must be sufficient to permit the untwisting, after setting, so that the yarn is non-lively at knitting, and to have a potential effect availableupon setrelease, to produce the desired liveliness of the yarn in the fabric. With filaments below l0 denier, e. g. at 1 or 2 denier, the twisting effect or liveliness in the fabric yarn may obviously be correspondingly higher: while at 20 and 40 denier, significant effects in wide gauge knit fabrics for example can be obtained with twists in the yarn ofthe fabric of less than 10 turns per inch, and even lower twists for greater diameters.

The removal of the liveliness from the twist-set yarn need not be accomplished upon the individual yarn. For example, two monolil or multifl yarns can be pre-set, twisted and Itwist-set, for example with bothv yarns having a left twist of 5l turns per inch. The two ends, without mechanical untwisting to remove the liveliness, can be plied together with, say, 8 turns of right-twist for l5 denier yarn: the bilar product` is then essentially dead and can be so knitted because the plying twist has removed the liveliness. Two such yarns A and B, respectively originally twisted right and left, can then be employed with a non-potential yarn C to produce a fabric. The fabric can then be treated for set-release whereupon the potential liveliness is developed in yarns A and B, with the respective effects of right-twist and left-twist of about 25 turns, and with a setting of the yarn C as described above. A like result can be attained with multifil yarns, e. g. two ends of 70 denier, V34 filament yarns.

The temperature conditioning given to the twisted material can be referred to as twist-setting in action upon yarns A and B: since its effect is to relieve some of the twisting stresses so that the yarns thus treated will not untwist completely when left free to adjust themselves, but will have stored within them a condition of potential or residual untwisting ability although this is not exhibited by physical tendency to untwist further; and since it involves .a second setting upon yarns A and B subsequent to the historical treatment which pre-sets the lament or subsequent to the preferred pre-setting for stabilizing various yarns to a condition of like prior history of heat treatment. It will be noted that if the third yarn C is capable of setting, such an action is established during the treatment which is given to the fabric.

The treatment of the yarns or fabric therefrom, by which such residual or potential twisting ability of the yarns is availed of for inducing liveliness therein, can be referred to as a releasing or set-releasing operation, since it causes residual or potential stress, resulting from the original twisting of the pre-set yarns, to become effective by release of the effect of the twist-setting.

Characteristic of this invention are the preparation of yarns A and B which can be knitted in essentially dead or non-lively condition but have within them the inherent 11 potential ability to attain lively or twisting states thereafter even when present in a fabric, and the preparation of a fabric from such yarns in conjunction with yarn C, and the production in such fabric of the lively state of the yarns A and B whereby the fabric contracts and assumes a correlated condition -of stretcha-bility.

The examples are illustrative; and the invention can obviously 'be practiced in many other ways in accordance with this disclosure and the scope of the claims.

I claim:

1. The method of making a stretchable fabric, which comprises knitting successionally with two dead yarns of stretched microcrystalline polymer material and having potential twists inherent therein, one said yarn having'a right twist potential and the other having left-twist potential, anda third dead yarn having no twist potential, whereby to produce a fabric, and then subjecting the fabric to a set releasing treatment effective to activate the inheren-t potential twist and thereby establish liveliness in the first said two yarns.

2. The method of making a stretchable fabric, which comprises knitting successionally with a first dead yarn having an inherent potential twist therein in one direction, then with a second dead yarn having a like inherent potential twist in the 4other direction, said first and second yarns being of stretched microcrystalline polymer material, and then with a third dead yarn having no twist potential, whereby to product a fabric; and then subjecting the fabric to a hea-t treatment eifective to activate the inherent potential twists in the first and second yarns. Y

3. The method as in claim 2, in which the heat treatment is effective to procure a setting in the third yarn.

4. The method of making a stretchable fabric, which comprises preparing two yarns of stretched microcrystalline polymer material and by pre-setting each at an elevated temperature; individually and oppositely twis-ting the two yarns, setting at a lower temperature, and untwisting until the yarns are dead, wherewith potential twists are present in the said two dead yarns; forming the said two yarns in dead condition together with a third dead yarn having no twist potential into a fabric having successive bands containing said three yarns; and subjecting the fabric to a heat treatment at a temperature less than said elevated temperature and effective to release at least a part of the setting effect in said first two yarns and procure liveliness therein.

5. The method as in claim 4, in which the liveliness procured in said first two yarns ycauses shrinkage of the fabric, and in which said heat treatment of the fabric 4is etfective to procure a set-ting effect upon the said third yarn.

6. The method as in claim 4, in which pairs of yarns of like-direction twist are brought together before the respective untwisting thereof.

7. A fabric produced by the method of claim 4.

8. A fabric produced by the method of claim 5.

9. The method as in claim 1, in which the said rst two dead yarns are each paired during knitting with a dead yarn having no twist potential.

10. A stocking produced by the method of claim 1.

11. The method as in claim 4, in which the said first two dead yarns having potential twist are each knit during fabrication with another yarn.

12. The method as in claim 4, in which the said rst two dead yarns having potential twist are each combined before the fabrication step with another yarn of like direction of twist, each composite yarn being individually twisted together in the tdirection opposite to the twist of the components thereof.

13. The method as in claim 4, in which, before the untwisting of the said rst two dead yarns having potential twist, the same are individually paired with other yarns which have 'been pre-set, twisted in the same respective direction and twist-set, and thereafter the pairs of yarns are individually untwisted to dead condition before the fabrication.

14. The method as in claim 4, in which the said rst two dead yarns having potential twist are each incorporated with a non-twisted and non-potential yarn during fabrication.

`15. The method of making a stretc'ha'ble fabric, which comprises preparing two yarns of stretched microcrystalline polymer material by presetting each at an elevated temperature; individually and oppositely twisting the two yarns, heating at a lower temperature for partially setting the twist, and untwisting until the yarns are dead, wherewith potential twists are present in the said two dead yarns; forming into a fabric the said two yarns in said dead condition together with a third dead yarn having no twist potential, including the introduction with each of said three yarns of a further dead yarn having no -twist potential wherewith the fabric has the said first three yarns in successive bands; and subjecting the fabric to a heat treatment at a temperature lessv than said elevated temperature and effective to release at least a part of each said potential twist in said first two yarns and procure liveliness therein.

References'Cited in the le of this patent UNITED STATES PATENTS 648,581 Benger May i, 1900 1,969,307 Kaufman Aug. 7, 1934 2,584,944 Tilles Feb. 5, 1952 2,736,945 Burleson et al Mar. 6, 1956 2,771,757 Burleson et al Nov. 27, 1956 FOREIGN PATENTS 1,027,272 Y France Feb. 11, 1953 

